This invention relates to a multispindle automatic lathe on which the gear trains for drive and feed systems are simplified and the main drum shaft (cam driving shaft) does not traverse between the gearbox and headstock.
When rod-shaped workpieces are machined continuously by using a plurality of cutting tools of different types, commonly used is a multispindle automatic lathe which rotates to index a spindle carrier carrying three to eight spindles for supporting the workpieces arranged in the same circumference at fixed intervals and which revolves to change the position of the spindles to carry out machining sequentially.
FIG. 6 is a partial sectional view of the spindle carrier of a conventional multispindle automatic lathe. As shown in FIG. 6, a spindle carrier 11 has a driving shaft 12 at its center, and a turning torque is given to this driving shaft 12 by a motor shown in FIG. 7. On the spindle carrier 11, a plurality of spindles 13 are pivotally carried at equal intervals in a concentric relation with the center of driving shaft 12. A gear 15 fixed to each spindle 13 engages with a gear 14 fixed to the driving shaft 12, so that the spindles 13 rotate simultaneously by the rotation of the driving shaft 12.
A workpiece W is supported by passing through the bore of each spindle 13 and rotates along with the rotation of the spindle 13. It is machined by a tool 17 carried on a cross tool slide 16 which moves in the direction perpendicular to the driving shaft 12 (the up and down direction in FIG. 6) and by a tool 19 carried on an end tool slide 18 which moves in the direction parallel to the driving shaft 12 (the right and left direction in FIG. 6).
The cross tool slide 16 and the end tool slide 18 are installed in plural numbers corresponding to the positions of the spindles 13. Workpieces on different spindles 13 simultaneously undergo different machining with these tools 17, 19. When the spindle carrier 11 rotates for indexing around the driving shaft 12, each spindle 13 revolves and changes its position in relation to the tools, so that each workpiece W is machined sequentially in a different manner until the workpiece is finished.
On this multispindle automatic lathe, the rotation of the spindle 13 and the feed of the cross tool slide 16 and the end tool slide 18 are performed by the transmission of power by means of gear trains shown in FIG. 7.
Specifically, the rotation of the motor 1 at a fixed speed is transmitted to a pulley shaft 31 via a belt 20 and pulleys 21,22. The rotation is then transmitted to the driving shaft 12 via a first meshing of gears 23 and 24, a second meshing of gears 25 and 26, and a third meshing of gears 27 and 28. The rotation of the driving shaft 12 is transmitted to a plurality of spindles via the meshing of gears 14 and 15. Thus, the spindle 13 rotates at a fixed speed by the motor 1 via many gears 23, 24, 25, 26, 27, 28.
Meanwhile, the rotation of the pulley shaft 31 is transmitted to a transmission shaft 43 via the meshing of bevel gears 35 and 36 so that the transmission shaft rotates at a high speed, or it is transmitted to transmission shaft 43 via the meshing of a gear 38 and a gear 37 which is mounted on the same shaft as gear 26, and that of gears 39 and 40, and that of a worm 41 and a worm wheel 42 so that the transmission shaft 43 rotates at a low speed.
A change from the power transmission by the bevel gear 36 to that by the worm wheel 42 and vice versa can be performed by means of a clutch 44 installed between the bevel gear 36 and the transmission shaft 43 and a clutch 45 installed between the worm wheel 42 and the transmission shaft 43.
The meshing of a worm 50 installed on the transmission shaft and a worm wheel 51 installed on a cam drum shaft also called a main drum shaft) 4 allows the cam drum shaft 4 to rotate at a reduced speed; as a result, a drum shaft 57 is rotated by the meshing of gears 52 and 53, and a cross drive shaft 58 is rotated by the meshing of gears 54, 55 and 56.
The rotation of the cross drive shaft 58 moves the above-mentioned cross tool slide 16 to produce, for example, the feed action of the tool 17 in the radial direction. The cam drum shaft 4 has a cylindrical cam 59 thereon, the rotation of which moves the above-mentioned end tool slide 18 to produce, for example, the feed action of the tool 19 in the axial direction.
The rotational speed of the spindle 13 is changed by changing the gear ratio; namely, by changing the combination of meshing gears of a spindle change gear 5 composed of the gears 25 and 26 and other gears not shown. The feed speed of the cross tool slide 16 is changed by changing the gear ratio; namely, by changing the combination of the meshing gears in a feed change gear set 6 composed of the gears 37 and 38 and other gears not shown or by changing the power transmission through the clutches 44 and 45.
Thus, the cutting conditions are changed by changing the gear ratio of the spindle change gear 5 and that of the feed change gear 6.
The multispindle automatic lathe using the conventional driving mechanism shown in FIG. 7, however, has some disadvantages.
To obtain the necessary rotational speed of spindles and the feed drive speed after the machining conditions are decided, the meshing of gears must be changed by determining the gear ratio of the spindle change gear 5 and the feed change gear 6. Therefore, the troublesome work of determining gear ratio and changing gear meshing is needed every time the machining conditions are changed.
Because the machining conditions are decided by the change gears 5 and 6, the rotational speed is limited by the combination of the number of gear teeth of these gears, so that proper machining conditions cannot be set freely, though the machining conditions can be selected to some degree.
The large-diameter cylindrical cam 59, which controls the movement of the end tool slide, requires much time in manufacturing and is difficult to handle because of its weight.
For the conventional driving mechanism, the cam drum shaft 4 is required which extends from a gearbox 101 to a headstock 102 (FIG. 8) incorporating the spindle carrier 11 and others because one motor 1 within the gearbox 101 performs all operations of driving the system. In this case, the cam drum shaft 4 lies under a tooling zone T, so that chips discharged from the upper portion are caught by the cam drum shaft 4, which disturbs the discharge of chips and sometimes requires stopping the machine to remove chips from the cam drum shaft.
Since the conventional driving mechanism has such a construction that the power is transmitted via many stages of gear trains, the number of parts of the machine itself is many, and it takes much time to assemble the machine, posing problems of high cost and low productivity.